Lithium batteries have become a useful and desirable energy source in recent years. Generally speaking lithium batteries are prepared from one or more lithium electrochemical cells containing electrochemically active (electroactive) materials. Such cells typically include a negative electrode, a positive electrode, and an electrolyte interposed between spaced apart positive and negative electrodes. By convention, the negative electrode is the electrode that acts as an anode (where oxidation occurs) on discharge, while the positive electrode is the one that acts as a cathode (where reduction occurs) on discharge.
Batteries with anodes of metallic lithium and containing metal chalcogenides cathode active material have received acceptance in industry and commerce.
So-called lithium ion batteries are well known. Lithium ion batteries have an insertion anode, such as a lithium metal chalcogenide, lithium metal oxide, coke or graphite. These types of electrodes are typically used with lithium-containing insertion cathodes to form an electroactive couple in a cell. The resulting cells are not charged in an initial condition. Before this type of cell can be used to deliver electrochemical energy, it must be charged. In the charging operation, lithium is transferred from the lithium-containing electrode cathode (the positive electrode) to the negative electrode. During discharge the lithium is transferred from the negative electrode back to the positive electrode. During a subsequent recharge, the lithium is transferred back to the negative electrode where it reinserts. Thus with each charge/discharge cycle, the lithium ions (Li+) are transported between the electrodes. Such rechargeable batteries having no free metallic species, are called rechargeable ion batteries or rocking chair batteries.
Known positive electrode active materials include LiCoO2, LiMn2O4, and LiNiO2. Lithium compounds containing cobalt are relatively expensive to synthesize due to the intermediates required, while successful synthesis of lithium-nickel compounds is relatively complex and difficult. Lithium-manganese compounds, such as LiMn2O4, are generally more economical to synthesize than the preceding material and result in a relatively economical positive electrode.
Unfortunately all of the foregoing materials have drawbacks as electroactive materials in electrochemical cells. Cells employing the foregoing materials in the cathode experience significant loss of charge capacity over repeated charge/discharge cycles, commonly referred to as cycle fading. Furthermore, the initial capacity available (amp hours/gram) from the materials is less than the theoretical capacity because significantly less than 1 atomic unit of lithium engages in the electrochemical reaction. This initial capacity value is significantly diminished during the first cycle of operation and diminishes even further on every successive cycle of operation. For LiNiO2 only about 0.5 atomic units of lithium is reversibly cycled during cell operation.
Many attempts have been made to reduce capacity fading, for example, as described in U.S. Pat. No. 4,828,834 by Niagara et al. However, the presently known and commonly used, alkali transition metal oxide compounds suffer from relatively low capacity. Therefore, there remains the difficulty of obtaining a lithium-containing electrode material having acceptable capacity without the disadvantage of significant capacity loss when used in a cell.
Alternative active materials for lithium ion applications are constantly being sought. In addition, there remains a need for providing an economical and reproducible synthesis method for such materials that will provide good quality material in suitable yields.